Number Seven (Daniel)
Daniel was the seventh Cylon model created by the Final Five, as revealed in the episode "No Exit". Ellen referred to Daniel as an "artist, and so sensitive to the world". She was very close to Daniel, which enraged Cavil; he felt that Daniel was Ellen's favorite child and became jealous. Cavil poisoned the amniotic fluid being used to mature the Daniel copies and then corrupted Daniel's genetic code. This sabotage meant that no further Daniel copies could be created - an elimination more permanent than the later model-wide boxing of the Number Threes. The Sevens were not mentioned again during Battlestar Galactica's remaining episodes. Because of the destruction of this model line, there were twelve models active throughout the series rather than thirteen.
Because of the nature of the character(s), fans began to speculate that Kara Thrace was a version of the corrupted Seven line, or that her father was. Ronald D. Moore stated in the podcast for "Islanded in a Stream of Stars" that Daniel is merely a plot device to explain the missing number and to expand on Cavil's character (noting that Daniel is essentially the Abel to Cavil's Cain). In the podcast for "No Exit", Moore described the Sevens as a springboard for Caprica, the BSG prequel, where Daniel Graystone is the name of a main character played by Eric Stoltz; this Daniel is the creator of the Colonial Centurions.
Number Sevens are never seen in the series, and therefore not played by any actor